Language is perhaps the biggest concept that separates humans from the rest of the animal kingdom. Yes, some creatures are capable of complex communication — dolphins, birds, etc. — but none reach the abilities of Homo sapiens. It’s no surprise then that the question of how we learn language has been something humans have wondered about for thousands of years. What makes it possible for a baby to go from babbling to fluent in just a few years?

From Ancient Greece to the modern day, people have come up with a number of theories about language acquisition. Here, we’ll explore some of the theories that have been decisively disproven, as well as the ones that are still hotly debated today. 

Types Of Language Acquisition

Depending on the circumstances, there are three different kinds of language acquisition. We’ll mostly focus on the first, but it’s worth noting that the phrase can refer to more than one thing.

• First-language acquisition — this is the first language a person learns, or a person’s native language.
• Second-language acquisition — while it says “second,” this refers to any language that you learn after the critical period of early learning ends.
• Bilingual acquisition — similar to first-language acquisition, except a child learns more than one language at the same time, which is extremely common.

While second-language acquisition is also an important field of study, first-language is a more difficult concept to explain. While a second-language learner is able to understand the concept of translation and grammar, a baby has to learn from scratch. How, exactly, does it work?

Theories Of First-Language Acquisition

Innate Knowledge

To start, we’re going all the way back to the fifth century BCE, when the philosopher Plato posited the idea of innate knowledge. He proposed that humans are born with many concepts in their head, and so the process of learning isn’t so much attaining new ideas, but recollecting the ones we already have. In this theory, then, a person doesn’t need to “acquire” a language because it’s already a part of their brain’s function. Though Plato contributed many important ideas to western philosophy, his idea of innate knowledge has mostly been disproven by modern neuroscience. Still, parts of this theory still play a role in influential language theories.

Cartesian Linguistics

This theory is named for René Descartes, and the main idea is that languages all have the same basic structure. This structure must necessarily reflect something in the way the brain works, meaning it’s not entirely a departure from the idea of innate knowledge. This idea was further honed by linguist Noam Chomsky, which we’ll discuss slightly further down.

Tabula Rasa

The idea that the human is a tabula rasa — a blank slate — has been proposed by many thinkers as far back as Aristotle, but the modern conception has mostly been formed by 17th century philosopher John Locke. This theory is essentially the exact opposite of innate knowledge, stating that when a person is born their brain is entirely moldable, and so they’re entirely a product of their environment.

Theory Of Behaviorism

The leading thinker on modern behaviorism is B.F. Skinner. In his book Verbal Behavior, he laid out his ideas that are essentially an expansion on the idea of the tabula rasa: humans are entirely a product of their environment. For Skinner, there is no innate system for humans creating knowledge. Instead, we learn from the “inputs” that we’re given; in other words, we are able to mimic the language spoken around us and slowly build our grammar and vocabulary.

Universal Grammar

Behaviorism — and B.F. Skinner — were strongly criticized by the thinker behind Universal Grammar: Noam Chomsky. One of his main criticisms is that it’s simply impossible for humans to learn a language so quickly unless there’s some sort of innate grammar. He calls this the poverty of the stimulus: there’s just no way for humans to become so fluent in a language by only listening to others speak.

Chomsky’s ideas are still hugely influential in the field of linguistics, but they’re not without controversy. Some linguists reject certain parts of it, while others think the whole idea of Universal Grammar should be thrown out. Recently, the growth of chat-based artificial intelligence has made some question Chomsky, with certain linguists claiming large language models are able to produce language very convincingly without having any sort of innate knowledge of language. Whether human and artificial intelligence are comparable, however, is still an open question.

Theories Of Second-Language Acquisition

While learning a first and second language does have quite a bit in common, there are some clear differences. When you’re learning Spanish, you can learn el carro means “the car,” but that’s different from having to figure out that “the car” refers to the very concept of a car. 

Chomsky’s Universal Grammar is applicable to second-language acquisition — the innate grammar carries over to learning a new language — but it’s far from the only model used. Here are a couple other popular models, though it’s by no means a comprehensive list.

The Acculturation Model

This model, put forward by linguist John Schumann, is primarily for people who are in a linguistic minority. The idea behind it is that learning a language is part of a larger process of “acculturation,” which is how someone — often someone who has immigrated to a new place — becomes integrated into the larger culture. Schumann’s ideas link the psychological process of language learning to a larger concept of adapting to new circumstances.

The Monitor Model

Also called the input hypothesis, the monitor model is largely ascribed to Steph Krashen, a linguist working in the 1970s and ‘80s. The idea that sets Krashen’s hypothesis apart from others is that he considered language learning — as in, the conscious project of learning a language using an app or a teacher or something else — to be entirely different from language acquisition, which is a more passive process. Another core concept is the idea that there is a natural order to learning a language, and you only acquire new concepts in a specific sequence. The reason it’s called the “input” hypothesis is, as Krashen states, because the only thing that matters in acquisition is the input you receive; your output, meaning your speaking in that language, does not contribute to “learning” in any meaningful way.

Despite all the theories, there’s still no universally accepted explanation for how humans acquire language. It’s something we can all do, but it’s also one of the most complex concepts known to humankind. It will likely always remain a bit of a mystery until we’re capable of fully mapping the brain.